What Is EVPN and Why It’s Revolutionizing Layer‑2 Networking

Part 1: What Is EVPN?

1. EVPN Basic Concept

EVPN (Ethernet Virtual Private Network) is a VPN technology for Layer‑2 interconnection. It uses a BGP‑like mechanism, extending BGP to carry reachability information, moving MAC learning and distribution from the data plane to the control plane.

2. EVPN Basic Topology

According to the connection between PE and CE, EVPN can be deployed in two topologies: CE multi‑attachment and CE single‑attachment.

CE2, CE3, and CE4 connected to a PE in a single‑attachment topology.

CE1 connected to PE1 and PE2, forming a multi‑attachment topology that supports load‑balancing.

EVPN defines an Ethernet Segment Identifier (ESI) for each PE‑CE link. All PEs attached to the same CE share the same ESI, while different CEs have different ESIs. The ESI is carried in routing updates so that PEs can recognize other PEs attached to the same CE.

Part 2: Basic Principles

3. Control Plane

EVPN extends BGP with new route types, allowing PEs to exchange MAC routes and learn remote user MAC addresses and the corresponding remote PE.

4. Forwarding Plane – Unicast Transmission

1. When PE1 receives a unicast packet from CE1, it pushes an EVPN label, then a public LDP‑LSP label, and encapsulates both PE1’s and PE2’s MAC addresses before sending the packet to PE2.

2. PE2 removes the encapsulation and forwards the packet to the appropriate EVPN site based on the EVPN label.

5. Forwarding Plane – Multicast Transmission

1. Upon receiving a multicast packet from CE1, PE1 replicates it into two copies, each encapsulated with an EVPN BUM label and a public LDP‑LSP label, then forwards them to remote PE2 and PE3.

2. PE2 and PE3 strip the encapsulation and deliver the multicast packet to the corresponding EVPN site using the EVPN BUM label.

Part 3: EVPN Advantages

6. Load Balancing and Link Utilization

Unlike traditional Layer‑2 solutions such as VPLS, EVPN’s multi‑attachment topology can be configured in an all‑active mode, allowing remote PEs to distribute traffic across all attached PEs, improving link utilization and transmission efficiency.

7. Reducing Full Mesh Overhead

VPLS requires a full mesh of pseudowire connections between PEs for each service instance. EVPN can use a route reflector to avoid establishing a full mesh, reducing the number of logical connections.

8. Faster Convergence

EVPN’s control‑plane based MAC learning accelerates routing convergence compared with data‑plane learning.

9. Reducing ARP Flooding

In VPLS, ARP broadcast is needed for MAC learning, consuming bandwidth and CPU. EVPN stores MAC information locally, allowing PEs to answer ARP requests directly and prevent large‑scale broadcasts.